1. Field of the Invention
The present invention relates to a radio receiver for estimating and compensating for in-phase/quadrature (IQ) mismatch.
2. Discussion of Related Art
In recent communication systems, a direct conversion reception method capable of reducing the number of components and having low complexity and low power consumption has been preferred. The direct conversion reception method converts a signal of a radio frequency (RF) band into a baseband by use of one mixer without involving an intermediate frequency. The mixer receives the RF signal and outputs signals of an in-phase (I) component and a quadrature (Q) component. Each signal is input to an analog-to-digital (A/D) converter through an amplifier and an analog filter. In this process, mismatch occurs in the signals of the I and Q components due to an analog circuit including a local oscillator, a mixer, an amplifier, and an analog filter. This mismatch reduces a signal to noise ratio of a received signal, thereby increasing a bit error rate (BER) and degrading the performance of a wireless communication receiver. To reduce the mismatch, errors of the I and Q components should be minimized when the analog circuit is designed. Also, when the analog circuit is designed, more precision is required and cost of the analog circuit increases.
To avoid these disadvantages, methods of estimating and compensating for the mismatch in a digital stage have been proposed. For example, there is a method using a pilot signal in an orthogonal frequency division multiplexing (OFDM) system or a method using a known signal in a system including a transmitter and a receiver. The method of estimating the mismatch by use of a specific pilot signal in a system supporting the OFDM scheme cannot be applied to a system with no pilot signal. There is a disadvantage in that the performance of estimating the mismatch is degraded due to a pilot signal estimation error. In the method proposed in a transceiver structure including both of the transmitter and the receiver, mismatch of the receiver is estimated by generating a specific signal through the transmitter and receiving the specific signal by the receiver in an RF stage. This method additionally requires a signal generator in a system only having a receiver such as a mobile broadcast receiver, and has a disadvantage in that the mismatch is not compensated for in real time during communication. Mismatch compensation methods proposed in the related art have a disadvantage in that time mismatch occurring due to a group delay difference of an analog filter between I and Q components or a circuit length difference in a broadband system having a high sampling frequency is not processed.